Hybrid vehicle drive controller

ABSTRACT

A drive control device for a hybrid vehicle is provided with a differential device including four rotary elements; and an engine, a first electric motor, a second electric motor and an output rotary member which are respectively connected to the four rotary elements. One of the four rotary elements is constituted by a rotary component of a first differential mechanism and a rotary component of a second differential mechanism selectively connected through a clutch, and one of the rotary components is selectively fixed to a stationary member through a brake. The drive control device comprises: an engine drive control portion configured to temporarily change an output torque of the engine when operating states of the clutch and the brake are changed in respective opposite directions to switch a vehicle drive mode from one of drive modes to another.

TECHNICAL FIELD

The present invention relates to an improvement of a drive controldevice for a hybrid vehicle.

BACKGROUND ART

There is known a hybrid vehicle which has at least one electric motor inaddition to an engine such as an internal combustion engine, whichfunctions as a vehicle drive power source. Patent Document 1 disclosesan example of such a hybrid vehicle, which is provided with an internalcombustion engine, a first electric motor and a second electric motor.This hybrid vehicle is further provided with a brake which is configuredto fix an output shaft of the above-described internal combustion engineto a stationary member, and an operating state of which is controlledaccording to a running condition of the hybrid vehicle, so as to improveenergy efficiency of the hybrid vehicle and to permit the hybrid vehicleto run according to a requirement by an operator of the hybrid vehicle.

PRIOR ART DOCUMENT Patent Document

-   Patent Document 1: JP-2008-265600 A1-   Patent Document 2: JP-4038183 B2

SUMMARY OF THE INVENTION Object Achieved by the Invention

By the way, the present applicant has been making an intensive study inan attempt to develop, as one form of a drive system for theabove-described hybrid vehicle, a hybrid vehicle drive system configuredto selectively establish a plurality of drive modes according torespective combinations of operating states of a clutch and a brakeincorporated therein, and to make a further improvement of theperformance of the drive system. In the process of the study, thepresent inventors discovered a risk of occurrence of problems such as avariation of a vehicle drive force and an excessive rise of a speed ofan electric motor, during a control of the operating states of theclutch and the brake to switch the drive system from one of the drivemodes to another.

The present invention was made in view of the background art describedabove. It is therefore an object of the present invention to provide adrive control device for a hybrid vehicle, which permits reduction ofoccurrence of such problems upon switching of a vehicle drive mode fromone of drive modes to another.

Means for Achieving the Object

The object indicated above is achieved according to a first aspect ofthe present invention, which provides a drive control device for ahybrid vehicle provided with: a first differential mechanism and asecond differential mechanism which have four rotary elements as awhole; and an engine, a first electric motor, a second electric motorand an output rotary member which are respectively connected to theabove-described four rotary elements, and wherein one of theabove-described four rotary elements is constituted by the rotaryelement of the above-described first differential mechanism and therotary element of the above-described second differential mechanismwhich are selectively connected to each other through a clutch, and oneof the rotary elements of the above-described first and seconddifferential mechanisms which are selectively connected to each otherthrough the above-described clutch is selectively fixed to a stationarymember through a brake, the drive control device being characterized bychanging a torque of the above-described engine when operating states ofthe above-described clutch and the above-described brake are changed inrespective opposite directions.

Advantages of the Invention

According to the first aspect of the invention described above, thehybrid vehicle is provided with: the first differential mechanism andthe second differential mechanism which have the four rotary elements asa whole; and the engine, the first electric motor, the second electricmotor and the output rotary member which are respectively connected tothe four rotary elements. One of the above-described four rotaryelements is constituted by the rotary element of the above-describedfirst differential mechanism and the rotary element of theabove-described second differential mechanism which are selectivelyconnected to each other through the clutch, and one of the rotaryelements of the above-described first and second differential mechanismswhich are selectively connected to each other through the clutch isselectively fixed to the stationary member through the brake. The drivecontrol device is configured to change the torque (output torque) of theabove-described engine when the operating states of the above-describedclutch and the above-described brake are changed in the respectiveopposite directions, namely, when a clutch-to-clutch control to switchthe clutch and the brake to respective different operating states isimplemented. According to this first aspect of the invention wherein theoutput torque of the above-described engine is controlled, it ispossible to reduce occurrence of problems such as an excessive rise of aspeed of the electric motor, as well as a variation of a vehicle driveforce, during a control to change the operating states of the clutch andthe brake in the respective opposite directions to switch the vehicledrive mode from one of drive modes to another. Namely, the presentinvention provides a drive control device for a hybrid vehicle, whichpermits reduction of occurrence of such problems upon switching of thevehicle drive mode from one mode to another.

According to a second aspect of the invention, the drive control deviceaccording to the first aspect of the invention is configured to increasean output torque of the above-described engine when the above-describedclutch which has been held in a released state and the above-describedbrake which has been held in an engaged state are respectively broughtinto an engaged state and a released state. According to this secondaspect of the invention, it is possible to reduce occurrence of theproblems such as the excessive rise of the speed of the electric motor,as well as the variation of the vehicle drive force, during a releasingaction of the above-described brake and an engaging action of theabove-described clutch to switch the vehicle drive mode from one drivemode to another.

According to a third aspect of the invention, the drive control deviceaccording to the first or second aspect of the invention is configuredsuch that the above-described first differential mechanism is providedwith a first rotary element connected to the above-described firstelectric motor, a second rotary element connected to the above-describedengine, and a third rotary element connected to the above-describedoutput rotary member, while the above-described second differentialmechanism is provided with a first rotary element connected to theabove-described second electric motor, a second rotary element, and athird rotary element, one of the second and third rotary elements beingconnected to the third rotary element of the above-described firstdifferential mechanism, and the above-described clutch is configured toselectively connect the second rotary element of the above-describedfirst differential mechanism, and the other of the second and thirdrotary elements of the above-described second differential mechanismwhich is not connected to the third rotary element of theabove-described first differential mechanism, to each other, while theabove-described brake is configured to selectively fix the other of thesecond and third rotary elements of the above-described seconddifferential mechanism which is not connected to the third rotaryelement of the above-described first differential mechanism, to thestationary member. According to this third aspect of the invention, itis possible to reduce occurrence of such problems upon switching of thevehicle drive mode from one mode to another in a drive system of thehybrid vehicle having a highly practical arrangement.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view for explaining an arrangement of a hybridvehicle drive system to which the present invention is suitablyapplicable;

FIG. 2 is a view for explaining major portions of a control systemprovided to control the drive system of FIG. 1;

FIG. 3 is a table indicating combinations of operating states of aclutch and a brake, which correspond to respective five drive modes ofthe drive system of FIG. 1;

FIG. 4 is a collinear chart having straight lines which permitindication thereon of relative rotating speeds of various rotaryelements of the drive system of FIG. 1, the collinear chartcorresponding to the modes 1 and 3 of FIG. 3;

FIG. 5 is a collinear chart having straight lines which permitindication thereon of relative rotating speeds of various rotaryelements of the drive system of FIG. 1, the collinear chartcorresponding to the mode 2 of FIG. 3;

FIG. 6 is a collinear chart having straight lines which permitindication thereon of relative rotating speeds of various rotaryelements of the drive system of FIG. 1, the collinear chartcorresponding to the mode 4 of FIG. 3;

FIG. 7 is a collinear chart having straight lines which permitindication thereon of relative rotating speeds of various rotaryelements of the drive system of FIG. 1, the collinear chartcorresponding to the mode 5 of FIG. 3;

FIG. 8 is a view for explaining transmission efficiency in the drivesystem of FIG. 1;

FIG. 9 is a functional block diagram for explaining major controlfunctions of an electronic control device of FIG. 2;

FIG. 10 is a collinear chart for explaining a control to increase anengine torque where the clutch is initially brought into its engagedstate to switch a vehicle drive mode of the drive system from the mode 3of FIG. 3 to the mode 4;

FIG. 11 is a collinear chart for explaining a control to bring the brakeinto its released state after the control to increase the engine torqueis implemented, to switch the vehicle drive mode from the mode 3 of FIG.3 to the mode 4;

FIG. 12 is a collinear chart for explaining a control to reduce anelectric motor torque where the brake is initially brought into itsreleased state to switch the vehicle drive mode from the mode 3 of FIG.3 to the mode 4;

FIG. 13 is a collinear chart for explaining a control to bring theclutch into its engaged state after a slipping speed of the clutch hasbeen substantially zeroed, to switch the vehicle drive mode from themode 3 of FIG. 3 to the mode 4;

FIG. 14 is a flow chart for explaining a major portion of one example ofa drive mode switching control implemented by the electronic controldevice of FIG. 2;

FIG. 15 is a flow chart for explaining a major portion of anotherexample of the drive mode switching control implemented by theelectronic control device of FIG. 2;

FIG. 16 is a schematic view for explaining an arrangement of a hybridvehicle drive system according to another preferred embodiment of thisinvention;

FIG. 17 is a schematic view for explaining an arrangement of a hybridvehicle drive system according to a further preferred embodiment of thisinvention;

FIG. 18 is a schematic view for explaining an arrangement of a hybridvehicle drive system according to a still further preferred embodimentof this invention;

FIG. 19 is a schematic view for explaining an arrangement of a hybridvehicle drive system according to a yet further preferred embodiment ofthis invention;

FIG. 20 is a schematic view for explaining an arrangement of a hybridvehicle drive system according to still another preferred embodiment ofthis invention;

FIG. 21 is a schematic view for explaining an arrangement of a hybridvehicle drive system according to yet another preferred embodiment ofthis invention;

FIG. 22 is a collinear chart for explaining an arrangement and anoperation of a hybrid vehicle drive system according to anotherpreferred embodiment of this invention;

FIG. 23 is a collinear chart for explaining an arrangement and anoperation of a hybrid vehicle drive system according to a furtherpreferred embodiment of this invention; and

FIG. 24 is a collinear chart for explaining an arrangement and anoperation of a hybrid vehicle drive system according to a still furtherpreferred embodiment of this invention.

MODE FOR CARRYING OUT THE INVENTION

According to the present invention, the first and second differentialmechanisms as a whole have four rotary elements while theabove-described clutch is placed in the engaged state. In one preferredform of the present invention, the first and second differentialmechanisms as a whole have four rotary elements while a plurality ofclutches, each of which is provided between the rotary elements of thefirst and second differential mechanisms and which includes theabove-described clutch, are placed in their engaged states. In otherwords, the present invention is suitably applicable to a drive controldevice for a hybrid vehicle which is provided with the first and seconddifferential mechanisms represented as the four rotary elementsindicated in a collinear chart, the engine, the first electric motor,the second electric motor and the output rotary member coupled to therespective four rotary elements, and wherein one of the four rotaryelements is selectively connected through the above-described clutch toanother of the rotary elements of the first differential mechanism andanother of the rotary elements of the second differential mechanism,while the rotary element of the first or second differential mechanismto be selectively connected to the above-indicated one rotary elementthrough the clutch is selectively fixed through the above-describedbrake to the stationary member.

In another preferred form of the present invention, the above-describedclutch and brake are hydraulically operated coupling devices operatingstates (engaged and released states) of which are controlled accordingto a hydraulic pressure. While wet multiple-disc type frictionalcoupling devices are preferably used as the clutch and brake, meshingtype coupling devices, namely, so-called dog clutches (claw clutches)may also be used. Alternatively, the clutch and brake may beelectromagnetic clutches, magnetic powder clutches and any otherclutches the operating states of which are controlled (which are engagedand released) according to electric commands.

The drive system to which the present invention is applicable is placedin a selected one of a plurality of drive modes, depending upon theoperating states of the above-described clutch and brake. Preferably, EVdrive modes in which at least one of the above-described first andsecond electric motors is used as a vehicle drive power source with theengine stopped include a mode 1 to be established in the engaged stateof the brake and in the released state of the clutch, and a mode 2 to beestablished in the engaged states of both of the clutch and brake.Further, hybrid drive modes in which the above-described engine isoperated while the above-described first and second electric motors areoperated to generate a vehicle drive force and/or an electric energy asneeded, include a mode 3 to be established in the engaged state of thebrake and in the released state of the clutch, a mode 4 to beestablished in the released state of the brake and the engaged state ofthe clutch, and a mode 5 to be established in the released states ofboth of the brake and clutch.

In a further preferred form of the invention, the rotary elements of theabove-described first differential mechanism, and the rotary elements ofthe above-described second differential mechanism are arranged as seenin the collinear charts, in the engaged state of the above-describedclutch and in the released state of the above-described brake, in theorder of the first rotary element of the first differential mechanism,the first rotary element of the second differential mechanism, thesecond rotary element of the first differential mechanism, the secondrotary element of the second differential mechanism, the third rotaryelement of the first differential mechanism, and the third rotaryelement of the second differential mechanism, where the rotating speedsof the second rotary elements and the third rotary elements of the firstand second differential mechanisms are indicated in mutually overlappingstates in the collinear charts.

In a still further preferred form of the invention, a torquecompensating control is implemented for compensation for an amount ofreduction of a torque of the engine due to a slipping action (partialengagement) of the clutch while the clutch which has been held in thereleased state and the brake which has been held in the engaged stateare respectively brought into the engaged and released states. Namely,an operation of the engine is controlled so as to increase a totaltorque of the engine by (so as to compensate for) an amount of reductiondue to the slipping action of the clutch when the total torque of theengine is decreased.

In a yet further preferred form of the invention, a torque reducingcontrol is implemented in relation to a control of a releasing action ofthe brake, to reduce a torque of the second electric motor by an amountof increase of a torque transmitted from the engine directly to theoutput rotary member, when the control to increase the output torque ofthe engine is implemented while the clutch which has been held in thereleased state and the brake which has been held in the engaged stateare respectively brought into the engaged and released states.Preferably, the brake is brought into the released state after thetorque of the second electric motor has been substantially zeroed.

In another preferred form of the invention, when the clutch and brakerespectively held in the released and engaged states are respectivelybrought into the engaged and released states, a control to bring theclutch into a fully engaged state is initiated after a slipping speed ofthe clutch, that is, a difference between rotating speeds of a pair ofrotary elements of the clutch has been substantially zeroed.

In yet another preferred form of the invention, a vehicle drive force,namely, a drive force generated by the output rotary member is heldconstant from a moment of initiation to a moment of termination of aclutch-to-clutch control to change the operating states of the clutchand brake in the respective opposite directions. That is, the operationof the engine, an operation of the second electric motor and theoperating states of the clutch and brake are controlled by the torqueincreasing control of the engine, the torque reducing control of thesecond electric motor and the operation controls of the clutch andbrake, which are implemented during the clutch-to-clutch control so asto maintain the drive force output from the output rotating member.

Referring to the drawings, preferred embodiments of the presentinvention will be described in detail. It is to be understood that thedrawings referred to below do not necessarily accurately representratios of dimensions of various elements.

FIRST EMBODIMENT

FIG. 1 is the schematic view for explaining an arrangement of a hybridvehicle drive system 10 (hereinafter referred to simply as a “drivesystem 10”) to which the present invention is suitably applicable. Asshown in FIG. 1, the drive system 10 according to the present embodimentis of a transversely installed type suitably used for an FF(front-engine front-drive) type vehicle, and is provided with a mainvehicle drive power source in the form of an engine 12, a first electricmotor MG1, a second electric motor MG2, a first differential mechanismin the form of a first planetary gear set 14, and a second differentialmechanism in the form of a second planetary gear set 16, which aredisposed on a common center axis CE. The drive system 10 is constructedsubstantially symmetrically with respect to the center axis CE. In FIG.1, a lower half of the drive system 10 is not shown. This descriptionapplies to other embodiments which will be described.

The engine 12 is an internal combustion engine such as a gasolineengine, which is operable to generate a drive force by combustion of afuel such as a gasoline injected into its cylinders. Each of the firstelectric motor MG1 and second electric motor MG2 is a so-calledmotor/generator having a function of a motor operable to generate adrive force, and a function of an electric generator operable togenerate a reaction force, and is provided with a stator 18, 22 fixed toa stationary member in the form of a housing (casing) 26, and a rotor20, 24 disposed radially inwardly of the stator 18, 22.

The first planetary gear set 14 is a single-pinion type planetary gearset which has a gear ratio ρ1 and which is provided with rotary elements(elements) consisting of a first rotary element in the form of a sungear S1; a second rotary element in the form of a carrier C1 supportinga pinion gear P1 such that the pinion gear P1 is rotatable about itsaxis and the axis of the planetary gear set; and a third rotary elementin the form of a ring gear R1 meshing with the sun gear S1 through thepinion gear P1. The second planetary gear set 16 is a single-pinion typeplanetary gear set which has a gear ratio ρ2 and which is provided withrotary elements (elements) consisting of: a first rotary element in theform of a sun gear S2; a second rotary element in the form of a carrierC2 supporting a pinion gear P2 such that the pinion gear P2 is rotatableabout its axis and the axis of the planetary gear set; and a thirdrotary element in the form of a ring gear R2 meshing with the sun gearS2 through the pinion gear P2.

The sun gear S1 of the first planetary gear set 14 is connected to therotor 20 of the first electric motor MG1. The carrier C1 of the firstplanetary gear set 14 is connected to an input shaft 28 which is rotatedintegrally with a crankshaft of the engine 12. This input shaft 28 isrotated about the center axis CE. In the following description, thedirection of extension of this center axis CE will be referred to as an“axial direction”, unless otherwise specified. The ring gear R1 of thefirst planetary gear set 14 is connected to an output rotary member inthe form of an output gear 30, and to the ring gear R2 of the secondplanetary gear set 16. The sun gear S2 of the second planetary gear set16 is connected to the rotor 24 of the second electric motor MG2.

The drive force received by the output gear 30 is transmitted to a pairof left and right drive wheels (not shown) through a differential geardevice not shown and axles not shown. On the other hand, a torquereceived by the drive wheels from a roadway surface on which the vehicleis running is transmitted (input) to the output gear 30 through thedifferential gear device and axles, and to the drive system 10. Amechanical oil pump 32, which is a vane pump, for instance, is connectedto one of opposite end portions of the input shaft 28, which one endportion is remote from the engine 12. The oil pump 32 is operated by theengine 12, to generate a hydraulic pressure to be applied to a hydrauliccontrol unit 60, etc. which will be described. An electrically operatedoil pump which is operated with an electric energy may be provided inaddition to the oil pump 32.

Between the carrier C1 of the first planetary gear set 14 and thecarrier C2 of the second planetary gear set 16, there is disposed aclutch CL which is configured to selectively couple these carriers C1and C2 to each other (to selectively connect the carriers C1 and C2 toeach other or disconnect the carriers C1 and C2 from each other).Between the carrier C2 of the second planetary gear set 16 and thestationary member in the form of the housing 26, there is disposed abrake BK which is configured to selectively couple (fix) the carrier C2to the housing 26. Each of these clutch CL and brake BK is ahydraulically operated coupling device the operating state of which iscontrolled (which is engaged and released) according to the hydraulicpressure applied thereto from the hydraulic control unit 60. While wetmultiple-disc type frictional coupling devices are preferably used asthe clutch CL and brake BK, meshing type coupling devices, namely,so-called dog clutches (claw clutches) may also be used. Alternatively,the clutch CL and brake BK may be electromagnetic clutches, magneticpowder clutches and any other clutches the operating states of which arecontrolled (which are engaged and released) according to electriccommands generated from an electronic control device 40.

As shown in FIG. 1, the drive system 10 is configured such that thefirst planetary gear set 14 and second planetary gear set 16 aredisposed coaxially with the input shaft 28 (disposed on the center axisCE), and opposed to each other in the axial direction of the center axisCE. Namely, the first planetary gear set 14 is disposed on one side ofthe second planetary gear set 16 on a side of the engine 12, in theaxial direction of the center axis CE. The first electric motor MG1 isdisposed on one side of the first planetary gear set 14 on the side ofthe engine 12, in the axial direction of the center axis CE. The secondelectric motor MG1 is disposed on one side of the second planetary gearset 16 which is remote from the engine 12, in the axial direction of thecenter axis CE. Namely, the first electric motor MG1 and second electricmotor MG2 are opposed to each other in the axial direction of the centeraxis CE, such that the first planetary gear set 14 and second planetarygear set 16 are interposed between the first electric motor MG1 andsecond electric motor MG2. That is, the drive system 10 is configuredsuch that the first electric motor MG1, first planetary gear set 14,clutch CL, second planetary gear set 16, brake BK and second electricmotor MG2 are disposed coaxially with each other, in the order ofdescription from the side of the engine 12, in the axial direction ofthe center axis CE.

FIG. 2 is the view for explaining major portions of a control systemprovided to control the drive system 10. The electronic control device40 shown in FIG. 2 is a so-called microcomputer which incorporates aCPU, a ROM, a RAM and an input-output interface and which is operable toperform signal processing operations according to programs stored in theROM while utilizing a temporary data storage function of the RAM, toimplement various drive controls of the drive system 10, such as a drivecontrol of the engine 12 and hybrid drive controls of the first electricmotor MG1 and second electric motor MG2. In the present embodiment, theelectronic control device 40 corresponds to a drive control device for ahybrid vehicle having the drive system 10. The electronic control device40 may be constituted by mutually independent control units as neededfor respective controls such as an output control of the engine 12 anddrive controls of the first electric motor MG1 and second electric motorMG2.

As indicated in FIG. 2, the electronic control device 40 is configuredto receive various signals from sensors and switches provided in thedrive system 10. Namely, the electronic control device 40 receives: anoutput signal of an accelerator pedal operation amount sensor 42indicative of an operation amount or angle A_(CC) of an acceleratorpedal (not shown), which corresponds to a vehicle output required by avehicle operator; an output signal of an engine speed sensor 44indicative of an engine speed N_(E), that is, an operating speed of theengine 12; an output signal of an MG1 speed sensor 46 indicative of anoperating speed N_(MG1) of the first electric motor MG1; an outputsignal of an MG2 speed sensor 48 indicative of an operating speedN_(MG2) of the second electric motor MG2; an output signal of an outputspeed sensor 50 indicative of a rotating speed N_(OUT) of the outputgear 30, which corresponds to a running speed V of the vehicle; outputsignals of wheel speed sensors 52 indicative of rotating speeds N_(W) ofwheels of the drive system 10; and an output signal of a battery SOCsensor 54 indicative of a stored electric energy amount (state ofcharge) SOC of a battery.

The electronic control device 40 is also configured to generate variouscontrol commands to be applied to various portions of the drive system10. Namely, the electronic control device 40 applies to an enginecontrol device 56 for controlling an output of the engine 12, followingengine output control commands for controlling the output of the engine12, which commands include: a fuel injection amount control signal tocontrol an amount of injection of a fuel by a fuel injecting device intoan intake pipe; an ignition control signal to control a timing ofignition of the engine 12 by an igniting device; and an electronicthrottle valve drive control signal to control a throttle actuator forcontrolling an opening angle θ_(TH) of an electronic throttle valve.Further, the electronic control device 40 applies command signals to aninverter 58, for controlling operations of the first electric motor MG1and second electric motor MG2, so that the first and second electricmotors MG1 and MG2 are operated with electric energies supplied theretofrom the battery through the inverter 58 according to the commandsignals to control outputs (output torques) of the electric motors MG1and MG2. Electric energies generated by the first and second electricmotors MG1 and MG2 are supplied to and stored in the battery through theinverter 58. Further, the electronic control device 40 applies commandsignals for controlling the operating states of the clutch CL and brakeBK, to linear solenoid valves and other electromagnetic control valvesprovided in the hydraulic control unit 60, so that hydraulic pressuresgenerated by those electromagnetic control valves are controlled tocontrol the operating states of the clutch CL and brake BK.

An operating state of the drive system 10 is controlled through thefirst electric motor MG1 and second electric motor MG2, such that thedrive system 10 functions as an electrically controlled differentialportion whose difference of input and output speeds is controllable. Forexample, an electric energy generated by the first electric motor MG1 issupplied to the battery or the second electric motor MG2 through theinverter 58. Namely, a major portion of the drive force of the engine 12is mechanically transmitted to the output gear 30, while the remainingportion of the drive force is consumed by the first electric motor MG1operating as the electric generator, and converted into the electricenergy, which is supplied to the second electric motor MG2 through theinverter 58, so that the second electric motor MG2 is operated togenerate a drive force to be transmitted to the output gear 30.Components associated with the generation of the electric energy and theconsumption of the generated electric energy by the second electricmotor MG2 constitute an electric path through which a portion of thedrive force of the engine 12 is converted into an electric energy whichis converted into a mechanical energy.

In the hybrid vehicle provided with the drive system 10 constructed asdescribed above, one of a plurality of drive modes is selectivelyestablished according to the operating states of the engine 12, firstelectric motor MG1 and second electric motor MG2, and the operatingstates of the clutch CL and brake BK. FIG. 3 is the table indicatingcombinations of the operating states of the clutch CL and brake BK,which correspond to the respective five drive modes of the drive system10. In this table, “o” marks represent an engaged state while blanksrepresent a released state. The drive modes EV-1 and EV-2 indicated inFIG. 3 are EV drive modes in which the engine 12 is held at rest whileat least one of the first electric motor MG1 and second electric motorMG2 is used as a vehicle drive power source. The drive modes HV-1, HV-2and HV-3 are hybrid drive modes (HV modes) in which the engine 12 isoperated as the vehicle drive power source while the first electricmotor MG1 and second electric motor MG2 are operated as needed togenerate a vehicle drive force and/or an electric energy. In thesehybrid drive modes, at least one of the first electric motor MG1 andsecond electric motor MG2 is operated to generate a reaction force orplaced in a non-load free state.

As is apparent from FIG. 3, the EV drive modes of the drive system 10 inwhich the engine 12 is held at rest while at least one of the firstelectric motor MG1 and second electric motor MG2 is used as the vehicledrive power source consist of; a mode 1 (drive mode 1) in the form ofthe drive mode EV-1 which is established in the engaged state of thebrake BK and in the released state of the clutch CL; and a mode 2 (drivemode 2) in the form of the drive mode EV-2 which is established in theengaged states of both of the brake BK and clutch CL. The hybrid drivemodes in which the engine 12 is operated as the vehicle drive powersource while the first electric motor MG1 and second electric motor MG2are operated as needed to generate a vehicle drive force and/or anelectric energy, consist of; a mode 3 (drive mode 3) in the form of thedrive mode HV-1 which is established in the engaged state of the brakeBK and in the released state of the clutch CL; a mode 4 (drive mode 4)in the form of the drive mode HV-2 which is established in the releasedstate of the brake BK and in the engaged state of the clutch CL; and amode 5 (drive mode 5) in the form of the drive mode HV-3 which isestablished in the released states of both of the brake BK and clutchCL.

FIGS. 4-7 are the collinear charts having straight lines which permitindication thereon of relative rotating speeds of the various rotaryelements of the drive system 10 (first planetary gear set 14 and secondplanetary gear set 16), which rotary elements are connected to eachother in different manners corresponding to respective combinations ofthe operating states of the clutch CL and brake BK. These collinearcharts are defined in a two-dimensional coordinate system having ahorizontal axis along which relative gear ratios ρ of the first andsecond planetary gear sets 14 and 16 are taken, and a vertical axisalong which the relative rotating speeds are taken. The collinear chartsindicate the relative rotating speeds when the output gear 30 is rotatedin the positive direction to drive the hybrid vehicle in the forwarddirection. A horizontal line X1 represents the rotating speed of zero,while vertical lines Y1 through Y4 arranged in the order of descriptionin the rightward direction represent the respective relative rotatingspeeds of the sun gear S1, sun gear S2, carrier C1 and ring gear R1.Namely, a solid line Y1 represents the relative rotating speed of thesun gear S1 of the first planetary gear set 14 (operating speed of thefirst electric motor MG1), a broken line Y2 represents the relativerotating speed of the sun gear S2 of the second planetary gear set 16(operating speed of the second electric motor MG2), a solid line Y3represents the relative rotating speed of the carrier C1 of the firstplanetary gear set 14 (operating speed of the engine 12), a broken lineY3′ represents the relative rotating speed of the carrier C2 of thesecond planetary gear set 16, a solid line Y4 represents the relativerotating speed of the ring gear R1 of the first planetary gear set 14(rotating speed of the output gear 30), and a broken line Y4′ representsthe relative rotating speed of the ring gear R2 of the second planetarygear set 16. In FIGS. 4-7, the vertical lines Y3 and Y3′ aresuperimposed on each other, while the vertical lines Y4 and Y4′ aresuperimposed on each other. Since the ring gears R1 and R2 are fixed toeach other, the relative rotating speeds of the ring gears R1 and R2represented by the vertical lines Y4 and Y4′ are equal to each other.

In FIGS. 4-7, a solid line L1 represents the relative rotating speeds ofthe three rotary elements of the first planetary gear set 14, while abroken line L2 represents the relative rotating speeds of the threerotary elements of the second planetary gear set 16. Distances betweenthe vertical lines Y1-Y4 (Y2-Y4′) are determined by the gear ratios ρ1and ρ2 of the first and second planetary gear sets 14 and 16. Describedmore specifically, regarding the vertical lines Y1, Y3 and Y4corresponding to the respective three rotary elements in the form of thesun gear S1, carrier C1 and ring gear R1 of the first planetary gear set14, a distance between the vertical lines Y1 and Y3 corresponds to “1”,while a distance between the vertical lines Y3 and Y4 corresponds to thegear ratio “ρ1”. Regarding the vertical lines Y2, Y3′ and Y4′corresponding to the respective three rotary elements in the form of thesun gear S2, carrier C2 and ring gear R2 of the second planetary gearset 16, a distance between the vertical lines Y2 and Y3′ corresponds to“1”, while a distance between the vertical lines Y3′ and Y4′ correspondsto the gear ratio “ρ2”. In the drive system 10, the gear ratio ρ2 of thesecond planetary gear set 16 is higher than the gear ratio ρ1 of thefirst planetary gear set 14 (ρ2>ρ1). The drive modes of the drive system10 will be described by reference to FIGS. 4-7.

The drive mode EV-1 indicated in FIG. 3 corresponds to the mode 1 (drivemode 1) of the drive system 10, which is preferably the EV drive mode inwhich the engine 12 is held at rest while the second electric motor MG2is used as the vehicle drive power source. FIG. 4 is the collinear chartcorresponding to the mode 1. Described by reference to this collinearchart, the carrier C1 of the first planetary gear set 14 and the carrierC2 of the second planetary gear set 16 are rotatable relative to eachother in the released state of the clutch CL. In the engaged state ofthe brake BK, the carrier C2 of the second planetary gear set 16 iscoupled (fixed) to the stationary member in the form of the housing 26,so that the rotating speed of the carrier C2 is held zero. In this mode1, the rotating direction of the sun gear S2 and the rotating directionof the ring gear R2 in the second planetary gear set 16 are opposite toeach other, so that when the second electric motor MG2 is operated togenerate a negative torque (acting in the negative direction), the ringgear R2, that is, the output gear 30 is rotated in the positivedirection by the generated negative torque. Namely, the hybrid vehicleprovided with the drive system 10 is driven in the forward directionwhen the negative torque is generated by the second electric motor MG2.In this case, the first electric motor MG1 is preferably held in a freestate. In this mode 1, the carriers C1 and C2 are permitted to berotated relative to each other, so that the hybrid vehicle can be drivenin the EV drive mode similar to an EV drive mode which is established ina vehicle provided with a so-called “THS” (Toyota Hybrid System) and inwhich the carrier C2 is fixed to the stationary member.

The drive mode EV-2 indicated in FIG. 3 corresponds to the mode 2 (drivemode 2) of the drive system 10, which is preferably the EV drive mode inwhich the engine 12 is held at rest while at least one of the firstelectric motor MG1 and second electric motor MG2 is used as the vehicledrive power source. FIG. 5 is the collinear chart corresponding to themode 2. Described by reference to this collinear chart, the carrier C1of the first planetary gear set 14 and the carrier C2 of the secondplanetary gear set 16 are not rotatable relative to each other in theengaged state of the clutch CL. Further, in the engaged state of thebrake BK, the carrier C2 of the second planetary gear set 16 and thecarrier C1 of the first planetary gear set 14 which is connected to thecarrier C2 are coupled (fixed) to the stationary member in the form ofthe housing 26, so that the rotating speeds of the carriers C1 and C2are held zero. In this mode 2, the rotating direction of the sun gear 51and the rotating direction of the ring gear R1 in the first planetarygear set 14 are opposite to each other, and the rotating direction ofthe sun gear S2 and the rotating direction of the ring gear R2 in thesecond planetary gear set 16 are opposite to each other, so that whenthe first electric motor MG1 and/or second electric motor MG2 is/areoperated to generate a negative torque (acting in the negativedirection), the ring gears R1 and R2 are rotated, that is, the outputgear 30 is rotated in the positive direction by the generated negativetorque. Namely, the hybrid vehicle provided with the drive system 10 isdriven in the forward direction when the negative torque is generated byat least one of the first electric motor MG1 and second electric motorMG2.

In the mode 2, at least one of the first electric motor MG1 and secondelectric motor MG2 may be operated as the electric generator. In thiscase, one or both of the first and second electric motors MG1 and MG2may be operated to generate a vehicle drive force (torque), at anoperating point assuring a relatively high degree of operatingefficiency, and/or with a reduced degree of torque limitation due toheat generation. Further, at least one of the first and second electricmotors MG1 and MG2 may be held in a free state, when the generation ofan electric energy by a regenerative operation of the electric motorsMG1 and MG2 is inhibited due to full charging of the battery. Namely,the mode 2 is an EV drive mode in which amounts of work to be assignedto the first and second electric motors MG1 and MG2 can be adjusted withrespect to each other, and which may be established under variousrunning conditions of the hybrid vehicle, or may be kept for arelatively long length of time. Accordingly, the mode 2 isadvantageously provided on a hybrid vehicle such as a plug-in hybridvehicle, which is frequently placed in an EV drive mode.

The drive mode HV-1 indicated in FIG. 3 corresponds to the mode 3 (drivemode 3) of the drive system 10, which is preferably the HV drive mode inwhich the engine 12 is used as the vehicle drive power source while thefirst electric motor MG1 and second electric motor MG2 are operated asneeded to generate a vehicle drive force and/or an electric energy. FIG.4 is the collinear chart corresponding to the mode 3. Described byreference to this collinear chart, the carrier C1 of the first planetarygear set 14 and the carrier C2 of the second planetary gear set 16 arerotatable relative to each other, in the released state of the clutchCL. In the engaged state of the brake BK, the carrier C2 of the secondplanetary gear set 16 is coupled (fixed) to the stationary member in theform of the housing 26, so that the rotating speed of the carrier C2 isheld zero. In this mode 3, the engine 12 is operated to generate anoutput torque by which the output gear 30 is rotated. At this time, thefirst electric motor MG1 is operated to generate a reaction torque inthe first planetary gear set 14, so that the output of the engine 12 canbe transmitted to the output gear 30. In the second planetary gear set16, the rotating direction of the sun gear S2 and the rotating directionof the ring gear R2 are opposite to each other, in the engaged state ofthe brake BK, so that when the second electric motor MG2 is operated togenerate a negative torque (acting in the negative direction), the ringgears R1 and R2 are rotated, that is, the output gear 30 is rotated inthe positive direction by the generated negative torque.

The drive mode HV-2 indicated in FIG. 3 corresponds to the mode 4 (drivemode 4) of the drive system 10, which is preferably the HV drive mode inwhich the engine 12 is used as the vehicle drive power source while thefirst electric motor MG1 and second electric motor MG2 are operated asneeded to generate a vehicle drive force and/or an electric energy. FIG.6 is the collinear chart corresponding to the mode 4. Described byreference to this collinear chart, the carrier C1 of the first planetarygear set 14 and the carrier C2 of the second planetary gear set 16 arenot rotatable relative to each other, in the engaged state of the clutchCL, that is, the carriers C1 and C2 are integrally rotated as a singlerotary element. The ring gears R1 and R2, which are fixed to each other,are integrally rotated as a single rotary element. Namely, in the mode 4of the drive system 10, the first planetary gear set 14 and secondplanetary gear set 16 function as a differential mechanism having atotal of four rotary elements. That is, the drive mode 4 is a compositesplit mode in which the four rotary elements consisting of the sun gearS1 (connected to the first electric motor MG1), the sun gear S2(connected to the second electric motor MG2), the rotary elementconstituted by the carriers C1 and C2 connected to each other (and tothe engine 12), and the rotary element constituted by the ring gears R1and R2 fixed to each other (and connected to the output gear 30) areconnected to each other in the order of description in the rightwarddirection as seen in FIG. 6.

In the mode 4, the rotary elements of the first planetary gear set 14and second planetary gear set 16 are preferably arranged as indicated inthe collinear chart of FIG. 6, that is, in the order of the sun gear S1represented by the vertical line Y1, the sun gear S2 represented by thevertical line Y2, the carriers C1 and C2 represented by the verticalline Y3 (Y3′), and the ring gears R1 and R2 represented by the verticalline Y4 (Y4′). The gear ratios ρ1 and ρ2 of the first and secondplanetary gear sets 14 and 16 are determined such that the vertical lineY1 corresponding to the sun gear S1 and the vertical line Y2corresponding to the sun gear S2 are positioned as indicated in thecollinear chart of FIG. 6, namely, such that the distance between thevertical lines Y1 and Y3 is longer than the distance between thevertical lines Y2 and Y3′. In other words, the distance between thevertical lines corresponding to the sun gear S1 and the carrier C1 andthe distance between the vertical lines corresponding to the sun gear S2and the carrier C2 correspond to “1”, while the distance between thevertical lines corresponding to the carrier C1 and the ring gear R1 andthe distance between the vertical lines corresponding to the carrier C2and the ring gear R2 correspond to the respective gear ratios ρ1 and ρ2.Accordingly, the drive system 10 is configured such that the gear ratioρ2 of the second planetary gear set 16 is higher than the gear ratio ρ1of the first planetary gear set 14.

In the mode 4, the carrier C1 of the first planetary gear set 14 and thecarrier C2 of the second planetary gear set 16 are connected to eachother in the engaged state of the clutch CL, so that the carriers C1 andC2 are rotated integrally with each other. Accordingly, either one orboth of the first electric motor MG1 and second electric motor MG2 canreceive a reaction force corresponding to the output of the engine 12.Namely, one or both of the first and second electric motors MG1 and MG2can be operated to receive the reaction force during an operation of theengine 12, and each of the first and second electric motors MG1 and MG2can be operated at an operating point assuring a relatively high degreeof operating efficiency, and/or with a reduced degree of torquelimitation due to heat generation.

For example, one of the first and second electric motors MG1 and MG2which is operable with a higher degree of operating efficiency ispreferentially operated to generate a reaction force, so that theoverall operating efficiency can be improved. When the hybrid vehicle isdriven at a comparatively high running speed V and at a comparativelylow engine speed N_(E), for instance, the operating speed N_(MG1) of thefirst electric motor MG1 may have a negative value, that is, the firstelectric motor MG1 may be operated in the negative direction. In thecase where the first electric motor MG1 generates the reaction force ofthe engine 12, the first electric motor MG1 is operated in the negativedirection so as to generate a negative torque with consumption of anelectric energy, giving rise to a risk of reduction of the operatingefficiency. In this respect, it will be apparent from FIG. 6 that in thedrive system 10, the operating speed of the second electric motor MG2indicated on the vertical line Y2 is less likely to have a negativevalue than the operating speed of the first electric motor MG1 indicatedon the vertical line Y1, and the second electric motor MG2 may possiblybe operated in the positive direction, during generation of the reactionforce. Accordingly, it is possible to improve the operating efficiencyto improve the fuel economy, by preferentially controlling the secondelectric motor MG2 so as to generate the reaction force, while theoperating speed of the first electric motor MG1 has a negative value.Further, where there is a torque limitation of one of the first electricmotor MG1 and second electric motor MG2 due to heat generation, it ispossible to ensure the generation of the reaction force required for theengine 12, by controlling the other electric motor so as to perform aregenerative operation or a vehicle driving operation, for providing anassisting vehicle driving force.

FIG. 8 is the view for explaining transmission efficiency of the drivesystem 10, wherein a speed ratio is taken along the horizontal axiswhile theoretical transmission efficiency is taken along the verticalaxis. The speed ratio indicated in FIG. 8 is a ratio of the input sidespeed of the first and second planetary gear sets 14 and 16 to theoutput side speed, that is, the speed reduction ratio, which is forexample, a ratio of the rotating speed of the input rotary member in theform of the carrier C1 to the rotating speed of the output gear 30 (ringgears R1 and R2). The speed ratio is taken along the horizontal axis inFIG. 8 such that the left side as seen in the view of FIG. 8 is a sideof high gear positions having comparatively low speed ratio values whilethe right side is a side of low gear positions having comparatively highspeed ratio values. Theoretical transmission efficiency indicated inFIG. 8 is a theoretical value of the transmission efficiency of thedrive system 10, which has a maximum value of 1.0 when an entirety ofthe drive force is mechanically transmitted from the first and secondplanetary gear sets 14 and 16 to the output gear 30, withouttransmission of an electric energy through the electric path.

In FIG. 8, a one-dot chain line represents the transmission efficiencyof the drive system 10 placed in the mode 3 (HV-1), while a solid linerepresents the transmission efficiency in the mode 4 (HV-2). Asindicated in FIG. 8, the transmission efficiency of the drive system 10in the mode 3 (HV-1) has a maximum value at a speed ratio value γ1. Atthis speed ratio value γ1, the operating speed of the first electricmotor MG1 (rotating speed of the sun gear S1) is zero, and an amount ofan electric energy transmitted through the electric path is zero duringgeneration of the reaction force, so that the drive force is onlymechanically transmitted from the engine 12 and the second electricmotor MG2 to the output gear 30, at an operating point corresponding tothe speed ratio value γ1. This operating point at which the transmissionefficiency is maximum while the amount of the electric energytransmitted through the electric path is zero will be hereinafterreferred to as a “mechanical point (mechanical transmission point)”. Thespeed ratio value γ1 is lower than “1”, that is, a speed ratio on anoverdrive side, and will be hereinafter referred to as a “firstmechanical transmission speed ratio value γ1”. As indicated in FIG. 8,the transmission efficiency in the mode 3 gradually decreases with anincrease of the speed ratio from the first mechanical transmission speedratio value γ1 toward the low-gear side, and abruptly decreases with adecrease of the speed ratio from the first mechanical transmission speedratio value γ1 toward the high-gear side.

In the mode 4 (HV-2) of the drive system 10, the gear ratios ρ1 and ρ2of the first planetary gear set 14 and second planetary gear set 16having the four rotary elements in the engaged state of the clutch CLare determined such that the operating speeds of the first electricmotor MG1 and second electric motor MG2 are indicated at respectivedifferent positions along the horizontal axis of the collinear chart ofFIG. 6, so that the transmission efficiency in the mode 4 has a maximumvalue at a mechanical point at a speed ratio value γ2, as well as at thespeed ratio value γ1, as indicated in FIG. 8. Namely, in the mode 4, therotating speed of the first electric motor MG1 is zero at the firstmechanical transmission speed ratio value γ1 at which the amount of theelectric energy transmitted through the electric path is zero duringgeneration of the reaction force by the first electric motor MG1, whilethe rotating speed of the second electric motor MG2 is zero at the speedratio value γ2 at which the amount of the electric energy transmittedthrough the electric path is zero during generation of the reactionforce by the second electric motor MG2. The speed ratio value γ2 will behereinafter referred to as a “second mechanical transmission speed ratiovalue γ2”. This second mechanical transmission speed ratio value γ2 issmaller than the first mechanical transmission speed ratio value γ1. Inthe mode 4, the drive system 10 has the mechanical point located on thehigh-gear side of the mechanical point in the mode 3.

As indicated in FIG. 8, the transmission efficiency in the mode 4 moreabruptly decreases with an increase of the speed ratio on a low-gearside of the first mechanical transmission speed ratio value γ1, than thetransmission efficiency in the mode 3. In a region of the speed ratiobetween the first mechanical transmission speed ratio value γ1 andsecond mechanical transmission speed ratio value γ2, the transmissionefficiency in the mode 4 changes along a concave curve. In this region,the transmission efficiency in the mode 4 is almost equal to or higherthan that in the mode 3. The transmission efficiency in the mode 4decreases with a decrease of the speed ratio from the second mechanicaltransmission speed ratio value γ2 toward the high-gear side, but ishigher than that in the mode 3. That is, the drive system placed in themode 4 has not only the first mechanical transmission speed ratio valueγ1, but also the second mechanical transmission speed ratio value γ2 onthe high-gear side of the first mechanical transmission speed ratiovalue γ1, so that the transmission efficiency of the drive system can beimproved in high-gear positions having comparatively low speed ratiovalues. Thus, a fuel economy during running of the vehicle at arelatively high speed is improved owing to an improvement of thetransmission efficiency.

As described above referring to FIG. 8, the transmission efficiency ofthe drive system 10 during a hybrid running of the vehicle with anoperation of the engine 12 used as the vehicle drive power source andoperations of the first and second electric motors MG1 and MG2 as neededto generate a vehicle drive force and/or an electric energy can beimproved by adequately switching the vehicle drive mode between the mode3 (HV-1) and mode 4 (HV-2). For instance, the mode 3 is established inlow-gear positions having speed ratio values lower than the firstmechanical transmission speed ratio value γ1, while the mode 4 isestablished in high-gear positions having speed ratio values higher thanthe first mechanical transmission speed ratio value γ1, so that thetransmission efficiency can be improved over a wide range of the speedratio covering the low-gear region and the high-gear region.

The drive mode HV-3 indicated in FIG. 3 corresponds to the mode 5 (drivemode 5) of the drive system 10, which is preferably the hybrid drivemode in which the engine 12 is operated as the vehicle drive powersource while the first electric motor MG1 is operated as needed togenerate a vehicle drive force and/or an electric energy. In this mode5, the engine 12 and first electric motor MG1 may be operated togenerate a vehicle drive force, with the second electric motor MG2 beingdisconnected from a drive system. FIG. 7 is the collinear chartcorresponding to this mode 5. Described by reference to this collinearchart, the carrier C1 of the first planetary gear set 14 and the carrierC2 of the second planetary gear set 16 are rotatable relative to eachother in the released state of the clutch CL. In the released state ofthe brake BK, the carrier C2 of the second planetary gear set 16 isrotatable relative to the stationary member in the form of the housing26. In this arrangement, the second electric motor MG2 can be held atrest while it is disconnected from the drive system (power transmittingpath).

In the mode 3 in which the brake BK is placed in the engaged state, thesecond electric motor MG2 is kept in an operated state together with arotary motion of the output gear 30 (ring gear R2) during running of thevehicle. In this operating state, the operating speed of the secondelectric motor MG2 may reach an upper limit value (upper limit) duringrunning of the vehicle at a comparatively high speed, or a rotary motionof the ring gear R2 at a high speed is transmitted to the sun gear S2.In this respect, it is not necessarily desirable to keep the secondelectric motor MG2 in the operated state during running of the vehicleat a comparatively high speed, from the standpoint of the operatingefficiency. In the mode 5, on the other hand, the engine 12 and thefirst electric motor MG1 may be operated to generate the vehicle driveforce during running of the vehicle at the comparatively high speed,while the second electric motor MG2 is disconnected from the drivesystem, so that it is possible to reduce a power loss due to dragging ofthe unnecessarily operated second electric motor MG2, and to eliminate alimitation of the highest vehicle running speed corresponding to thepermissible highest operating speed (upper limit of the operating speed)of the second electric motor MG2.

It will be understood from the foregoing description, the drive system10 is selectively placed in one of the three hybrid drive modes in whichthe engine 12 is operated as the vehicle drive power source, namely, inone of the drive mode HV-1 (mode 3), drive mode HV-2 (mode 4) and drivemode HV-3 (mode 5), which are selectively established by respectivecombinations of the engaged and released states of the clutch CL andbrake BK. Accordingly, the transmission efficiency can be improved toimprove the fuel economy of the vehicle, by selectively establishing oneof the three hybrid drive modes according to the vehicle running speedand the speed ratio, in which the transmission efficiency is thehighest.

FIG. 9 is the functional block diagram for explaining major controlfunctions of the electronic control device 40. A drive mode determiningportion 70 is configured to determine one of the drive modes of thedrive system 10 to be established. The drive mode determining portion 70is basically configured to select one of the modes 1-5 described aboveby reference to FIG. 3, according to a predetermined relationship and onthe basis of the accelerator pedal operation amount A_(CC) detected bythe accelerator pedal operation amount sensor 42, the vehicle runningspeed V corresponding to the output speed N_(OUT) detected by the outputspeed sensor 50, and the stored electric energy amount SOC detected bythe battery SOC sensor 54, for example.

Preferably, the drive mode determining portion 70 selects the EV drivemode in the form of the mode 1 or 2 in which the engine 12 is held atrest, when the stored electric energy amount SOC detected by the batterySOC sensor 54 is not smaller than a predetermined threshold value. Uponstarting of the hybrid vehicle, namely, upon a releasing action of abrake pedal (not shown) (from the operated position to the non-operatedposition) when the vehicle running speed V corresponding to the outputspeed N_(OUT) detected by the output speed sensor 50 is zero while thestored electric energy amount SOC detected by the battery SOC sensor 54is not smaller than the above-indicated threshold value, for instance,the drive mode determining portion 70 selects the EV drive mode in theform of the mode 1 in which the engine 12 is held at rest while thefirst electric motor MG1 is primarily used as the vehicle drive powersource.

Preferably, the drive mode determining portion 70 selects one of thehybrid drive modes in the form of the drive modes 3-5 in which theengine 12 is operated as the vehicle drive power source, when the storedelectric energy amount SOC detected by the battery SOC sensor 54 issmaller than a predetermined threshold value. Where the drive system 10should be placed in a lower-gear position (lower-speed position orhigher-speed-ratio position) as compared with the position of the firstmechanical transmission speed ratio value γ1 described above byreference to FIG. 8, for example, while the stored electric energyamount SOC detected by the battery SOC sensor 54 is smaller than thepredetermined threshold value, the drive mode determining portion 70selects the mode 3 (HV-1). Where the drive system 10 should be placed ina higher-gear position (higher-speed position or lower-speed-ratioposition) as compared with the position of the first mechanicaltransmission speed ratio value γ1 described above by reference to FIG.8, on the other hand, the drive mode determining portion 70 selects themode 4 (HV-2). In addition, the drive mode determining portion 70selects one of the drive modes according to the specific running stateof the hybrid vehicle provided with the drive system 10, so as toimprove the transmission efficiency and the fuel economy of the engine12.

The electric motor operation control portion 72 is configured to controlthe operations of the first and second electric motors MG1 and MG2through the inverter 58. Described more specifically, the electric motoroperation control portion 72 controls the amounts of electric energy tobe supplied from the battery (not shown) to the first and secondelectric motors MG1 and MG2 through the inverter 58, so that each of thefirst and second electric motors MG1 and MG2 provides a required output,that is, a target torque (target electric motor output). When the firstor second electric motor MG1, MG2 is operated as an electric generator,the electric motor operation control portion 72 implements a control forstoring an electric energy generated by the first or second electricmotor MG1, MG2, in the battery through the inverter 58.

A clutch engagement control portion 74 is configured to control theoperating state of the clutch CL through the hydraulic control unit 60.For instance, the clutch engagement control portion 74 controls anoutput hydraulic pressure of a solenoid control valve provided in thehydraulic control unit 60 to control the clutch CL, so as to place theclutch CL in an engaged state or a released state. A brake engagementcontrol portion 76 is configured to control the operating state of thebrake BK through the hydraulic control unit 60. For instance, the brakeengagement control portion 76 controls an output hydraulic pressure of asolenoid control valve provided in the hydraulic control unit 60 tocontrol the brake BK, so as to place the brake BK in an engaged state ora released state. The clutch engagement control portion 74 and the brakeengagement control portion 76 are basically configured to control theoperating states of the clutch CL and the brake BK to establish thedrive mode selected by the drive mode determining portion 70. Namely,the clutch and brake engagement control portions 74 and 76 establish oneof the combinations of the operating states of the clutch CL and thebrake BK indicated in FIG. 3, which corresponds to one of the modes 1-5to be established.

An engine drive control portion 78 is configured to control an operationof the engine 12 through the engine control device 56. For instance, theengine drive control portion 78 commands the engine control device 56 tocontrol an amount of supply of a fuel by a fuel injecting device of theengine 12 into an intake pipe, for example, a timing of ignition(ignition timing) of the engine 12 by an igniting device, and an openingangle θ_(TH) of an electronic throttle valve, so that the engine 12generates a required output, that is, a target torque (target engineoutput). In the hybrid drive modes in which the engine 12 is operatedwhile the first and second electric motors MG1 and MG2 are used as thevehicle drive power source, a required vehicle drive force to begenerated by the drive system 10 (output gear 30) is calculated on thebasis of the accelerator pedal operation amount A_(CC) detected by theaccelerator pedal operation amount sensor 42, and the vehicle runningspeed V corresponding to the output speed N_(OUT) detected by the outputspeed sensor 50, for example. The operations of the first and secondelectric motors MG1 and MG2 are controlled by an electric motoroperation control portion 72, while the operation of the engine 12 iscontrolled by the engine drive control portion 78, so that thecalculated required vehicle drive force is obtained by the output torqueof the engine 12 and the output torques of the first and second electricmotors MG1 and MG2.

The engine drive control portion 78 controls the output torque of theengine 12 when a so-called “clutch-to-clutch” control to change theoperating states of the clutch CL and the brake BK in respectiveopposite directions is implemented to switch the drive system 10 fromone of the drive modes to another. This “clutch-to-clutch” control is aswitching control to bring a coupling element (in the form of the clutchCL or brake BK) which has been held in its engaged state, into itsreleased state, and to bring another coupling element which has beenheld in its released state, into its engaged state. Described morespecifically, the switching control is either a control to bring theclutch CL and brake BK which have been respectively held in the releasedand engaged states, into the engaged and released states, or a controlto bring the clutch CL and brake BK which have been respectively held inthe engaged and released states, into the released and engaged states.For example, the clutch-to-clutch control is implemented when thevehicle drive mode is switched from the mode 3 (HV-1) to the mode 4(HV-2), or from the mode 4 to the mode 3.

The engine drive control portion 78 is preferably configured toimplement a control to increase the output torque of the engine 12 whenthe clutch CL which has been held in the released state and the brake BKwhich has been held in the engaged state are respectively brought intothe engaged and released states. When the drive mode determining portion70 has determined a requirement for switching the vehicle drive modefrom the mode 3 (HV-1) to the mode 4 (HV-2), for instance, the enginedrive control portion 78 implements the control to increase the outputtorque of the engine 12. Namely, the engine drive control portion 78commands the engine control device 56 to control the operation of theengine 12 so as to temporarily increase the output torque of the engine12 (engine torque T_(E)) during the clutch-to-clutch control to switchthe vehicle drive mode from the mode 3 to the mode 4.

When the vehicle drive mode is switched from the mode 3 (HV-1) to themode 4 (HV-2), the clutch engagement control portion 74 and the brakeengagement control portion 76 preferably initiate an engaging action ofthe clutch CL, and bring the brake BK into the released state after theengaging action of the clutch CL has proceeded to a predetermined stage.In this preferred form of control, the engine drive control portion 78preferably implements a torque compensating control for compensation foran amount of reduction of the torque of the engine 12 due to a slippingaction (partial engagement) of the clutch CL (during transition of theclutch CL from a fully released state to a fully engaged state). FIG. 10is the collinear chart for explaining a control to increase the enginetorque where the clutch CL is initially brought into its engaged stateto switch the vehicle drive mode from the mode 3 of FIG. 3 to the mode4. In FIG. 10 (in FIGS. 11-13, as well), white arrows represent thetorques acting on the various rotary elements. It will be understoodfrom FIG. 10 that where the clutch CL is brought into the engaged statebefore the brake BK is brought into the released state, in theclutch-to-clutch control to switch the vehicle drive mode from the mode3 to the mode 4, the slipping action (an increase of the torquecapacity) of the clutch CL causes generation of a torque in the negativedirection of the engine 12, resulting in reduction of a total torque ofthe engine 12. Preferably, the engine drive control portion 78 increasesthe torque of the engine 12 by an amount of reduction of the totaltorque of the engine 12 due to the slipping action of the clutch CL, sothat the total torque of the engine 12 is held substantially constant.According to this control, the vehicle drive force, namely, a driveforce generated by the output gear 30 is held constant (the vehicledrive force is kept unchanged), as indicated by a white broken-linearrow in FIG. 10. In other words, an increase (an amount and a rate ofincrease) of the torque of the engine 12 is controlled so that thevehicle drive force is held constant.

When the control to increase the output torque of the engine 12 isimplemented by the engine drive control portion 78 while the clutch CLwhich has been held in the released state and the brake BK which hasbeen held in the engaged state are respectively brought into the engagedand released states, the electric motor operation control portion 72preferably implements a torque reducing control in relation to thecontrol of the releasing action of the brake BK, to reduce the torque ofthe second electric motor MG2 by an amount of increase of the torquetransmitted from the engine 12 directly to the output gear 30. FIG. 11is the collinear chart for explaining a control to bring the brake BKinto the released state after the control to increase the engine torqueis implemented, to switch the vehicle drive mode system from the mode 3to the mode 4. It will be understood from FIG. 11 that where the controlto increase the output torque of the engine 12 is implemented when thevehicle drive mode is switched from the mode 3 to the mode 4, there is arisk of an excessive rise of the operating speed of the second electricmotor MG2 (an increase of the operating speed in the negative direction)due to reduction of the torque transmitted through the brake BK in theprocess of its releasing action. Preferably, the electric motoroperation control portion 72 reduces the torque (negative torque) of thesecond electric motor MG2 by an amount of increase of the torquetransmitted from the engine 12 to the output gear 30, as a result of anincrease of the torque of the engine 12. Preferably, the electric motoroperation control portion 72 reduces the torque of the second electricmotor MG2 to substantially zero before the releasing action of the brakeBK is initiated. Namely, the brake engagement control portion 76initiates the releasing action (substantially releasing action) of thebrake BK after the torque of the second electric motor MG2 has beensubstantially zeroed according to the above-described torque reducingcontrol. Accordingly, the vehicle drive force namely, the drive forcegenerated by the output gear 30 is held constant (the vehicle driveforce is kept unchanged), as indicated by a white broken-line arrow inFIG. 11. In other words, a reduction (an amount and a rate of reduction)of the torque of the second electric motor MG2 is controlled so that thevehicle drive force is held constant.

When the vehicle drive mode is switched from the mode 3 (HV-1) to themode 4 (HV-2), the clutch engagement control portion 74 and the brakeengagement control portion 76 preferably initiate the releasing actionof the brake BK, and bring the clutch CL into the engaged state afterthe releasing action of the brake BK has proceeded to a predeterminedstage. In this preferred form of control, the electric motor operationcontrol portion 72 preferably implements a control to reduce the torqueof the second electric motor MG2 during a slipping action (partialengagement) of the brake BK (during transition of the brake BK from thefully released state to the fully engaged state). FIG. 12 is thecollinear chart for explaining the control to reduce the MG2 torquewhere the brake BK is initially brought into its engaged state to switchthe vehicle drive mode from the mode 3 of FIG. 3 to the mode 4. It willbe understood from FIG. 12 that the torque transmitted through the brakeBK is reduced as a result of the transition from the fully engaged stateto the slipping action (partial engagement) to switch the vehicle drivemode from the mode 3 to the mode 4. Accordingly, the reaction force ofthe second electric motor MG2 is reduced, giving rise to a risk of anexcessive rise of the operating speed of the second electric motor MG2(an increase of the operating speed in the negative direction), asindicated by a broken line L2′ in FIG. 12. Preferably, the electricmotor operation control portion 72 reduces the torque (negative torque)of the second electric motor MG2, in relation to the releasing action ofthe brake BK. Before or after this torque reducing control, the enginedrive control portion 78 implements the control to increase the outputtorque of the engine 12. According to the controls indicated above, thevehicle drive force, namely, the drive force generated by the outputgear 30 is held constant (the vehicle drive force is kept unchanged), asindicated by a white broken-line arrow in FIG. 12. In other words, theincrease (amount and rate of increase) of the torque of the engine 12,and the reduction (amount and rate of reduction) of the torque of thesecond electric motor MG2, are controlled so that the vehicle driveforce is held constant.

Where the brake BK is initially brought into the released state toswitch the vehicle drive mode from the mode 3 (HV-1) to the mode 4(HV-2), the clutch engagement control portion 74 preferably initiatesthe engaging action (substantially engaging action) of the clutch CLwhen a slipping speed of the clutch CL has been substantially zeroed.That is, the clutch engagement control portion 74 initiates the engagingaction of the clutch CL when a difference ΔN (=|N_(C1)−N_(C2)| between arotating speed N_(C1) of the carrier C1 of the first planetary gear set14 indicated on the vertical line Y3 in FIG. 13 and a rotating speedN_(C2) of the carrier C2 of the second planetary gear set 16 indicatedon the vertical line Y3′ in FIG. 13 has been reduced below apredetermined extremely small threshold value (substantially zero). Therotating speed N_(C1) of the carrier C1 of the first planetary gear set14 is calculated on the basis of the engine speed N_(E), the MG1 speedN_(MG1) and the output speed N_(OUT). The rotating speed N_(C2) of thecarrier C2 of the second planetary gear set 16 is calculated on thebasis of the MG2 speed N_(MG2) and the output speed N_(OUT). Accordingto this control, the vehicle drive force, namely, the drive forcegenerated by the output gear 30 is held constant (the vehicle driveforce is kept unchanged), as indicated by a white broken-line arrow inFIG. 13. By initiating the engaging action of the clutch CL after theslipping speed of the clutch CL has been substantially zeroed, it ispossible to effectively prevent deterioration of durability of theclutch CL.

FIG. 14 is the flow chart for explaining a major portion of an exampleof a drive mode switching control implemented by the electronic controldevice 40. The drive mode switching control is repeatedly implementedwith a predetermined cycle time.

The drive mode switching control is initiated with step SA1 (“step”being hereinafter omitted), to determine whether the vehicle drive modeis required to be switched from the mode 3 (HV-1) to the mode 4 (HV-2).If a negative determination is obtained in SA1, the present routine isterminated. If an affirmative determination is obtained in SA1, on theother hand, the control flow goes to SA2 to implement the control tobring the clutch CL into the engaged state. Then, the control flow goesto SA3 to implement the control to increase the output torque of theengine 12. For instance, the output torque of the engine 12 is increasedby an amount of reduction of the torque of the engine 12 due to theslipping action of the clutch CL. The control flow then goes to SA4 toimplement the control to reduce the torque of the second electric motorMG2. For example, the torque of the second electric motor MG2 is reducedby an amount of increase of the torque transmitted from the engine 12directly to the output gear 30, as a result of the control in SA3. Then,the control flow goes to SA5 to determine whether the torque of thesecond electric motor MG2 has been substantially zeroed. If a negativedetermination is obtained in SA5, the control flow goes back to SA2. Ifan affirmative determination is obtained in SA5, on the other hand, thecontrol flow goes to SA6 to implement the control to bring the brake BKinto the released state. Then, the control flow goes to SA7 to determinewhether the vehicle drive mode has been switched from the mode 3 (HV-1)to the mode 4 (HV-2). If a negative determination is obtained in SA7,the control flow goes back to SA2. If an affirmative determination isobtained in SA7, on the other hand, the present routine is terminated.

FIG. 15 is the flow chart for explaining a major portion of anotherexample of the drive mode switching control implemented by theelectronic control device 40. The drive mode switching control isrepeatedly implemented with a predetermined cycle time.

The drive mode switching control is initiated with SB1 to determinewhether the vehicle drive mode is required to be switched from the mode3 (HV-1) to the mode 4 (HV-2). If a negative determination is obtainedin SB1, the present routine is terminated. If an affirmativedetermination is obtained in SB1, on the other hand, the control flowgoes to SB2 to implement the control to bring the brake BK into thereleased state. Then, the control flow goes to SB3 to implement thecontrol to increase the output torque of the engine 12. The control flowthen goes to SB4 to implement the control to reduce the torque of thesecond electric motor MG2. Then, the control flow goes to SB5 todetermine whether the slipping speed of the clutch CL, that is, thedifference ΔN between the rotating speed N_(C1) of the carrier C1 of thefirst planetary gear set 14 and the rotating speed N_(C2) of the carrierC2 of the second planetary gear set 16 has been substantially zeroed. Ifa negative determination is obtained in SB5, the control flow goes backto SB2. If an affirmative determination is obtained in SB5, on the otherhand, the control flow goes to SB6 to implement the control to bring theclutch CL into the fully engaged state. Then, the control flow goes toSB7 to determine whether the vehicle drive mode has been switched fromthe mode 3 (HV-1) to the mode 4 (HV-2). If a negative determination isobtained in SB7, the control flow goes back to SB2. If an affirmativedetermination is obtained in SB7, on the other hand, the present routineis terminated.

It will be understood from the foregoing description by reference toFIGS. 14 and 15 that SA1 and SB1 correspond to the operation of thedrive mode determining portion 70, and SA4 and SB4 correspond to theoperation of the electric motor operation control portion 72, and thatSA2 and SB6 correspond to the operation of the clutch engagement controlportion 74, and SA6 and SB2 correspond to the operation of the brakeengagement control portion 76, while SA3 and SB3 correspond to theoperation of the engine drive control portion 78.

Other preferred embodiments of the present invention will be describedin detail by reference to the drawings. In the following description,the same reference signs will be used to identify the same elements inthe different embodiments, which will not be described redundantly.

SECOND EMBODIMENT

FIGS. 16-21 are the schematic views for explaining arrangements ofrespective hybrid vehicle drive systems 100, 110, 120, 130, 140 and 150according to other preferred modes of this invention. The hybrid vehicledrive control device of the present invention is also applicable todrive systems such as the drive system 100 shown in FIG. 16 and thedrive system 110 shown in FIG. 17, which have respective differentarrangements of the first electric motor MG1, first planetary gear set14, second electric motor MG2, second planetary gear set 16, clutch CLand brake BK in the direction of the center axis CE. The present hybridvehicle drive control device is also applicable to drive systems such asthe drive system 120 shown in FIG. 18, which have a one-way clutch OWCdisposed between the carrier C2 of the second planetary gear set 16 andthe stationary member in the form of the housing 26, in parallel withthe brake BK, such that the one-way clutch OWC permits a rotary motionof the carrier C2 relative to the housing 26 in one of oppositedirections and inhibits a rotary motion of the carrier C2 in the otherdirection. The present hybrid vehicle drive control device is furtherapplicable to drive systems such as the drive system 130 shown in FIG.19, the drive system 140 shown in FIG. 20 and the drive system 150 shownin FIG. 21, each of which is provided with a second differentialmechanism in the form of a second planetary gear set 16′ of adouble-pinion type, in place of the second planetary gear set 16 of asingle-pinion type. This second planetary gear set 16′ is provided withrotary elements (elements) consisting of a first rotary element in theform of a sun gear S2′; a second rotary element in the form of a carrierC2′ supporting a plurality of pinion gears P2′ meshing with each othersuch that each pinion gear P2′ is rotatable about its axis and the axisof the planetary gear set; and a third rotary element in the form of aring gear R2′ meshing with the sun gear S2′ through the pinion gearsP2′.

THIRD EMBODIMENT

FIGS. 22-24 are the collinear charts for explaining arrangements andoperations of respective hybrid vehicle drive systems 160, 170 and 180according to other preferred embodiments of this invention in place ofthe drive system 10. In FIGS. 22-24, the relative rotating speeds of thesun gear S1, carrier C1 and ring gear R1 of the first planetary gear set14 are represented by the solid line L1, while the relative rotatingspeeds of the sun gear S2, carrier C2 and ring gear R2 of the secondplanetary gear set 16 are represented by the broken line L2, as in FIGS.4-7. In the hybrid vehicle drive system 160 shown in FIG. 22, the sungear S1, carrier C1 and ring gear R1 of the first planetary gear set 14are respectively connected to the first electric motor MG1, engine 12and second electric motor MG2, while the sun gear S2, carrier C2 andring gear R2 of the second planetary gear set 16 are respectivelyconnected to the second electric motor MG2 and output gear 30, and tothe housing 26 through the brake BK. The sun gear S1 and the ring gearR2 are selectively connected to each other through the clutch CL. Thering gear R1 and the sun gear S2 are connected to each other. In thehybrid vehicle drive system 170 shown in FIG. 23, the sun gear S1,carrier C1 and ring gear R1 of the first planetary gear set 14 arerespectively connected to the first electric motor MG1, output gear 30and engine 12, while the sun gear S2, carrier C2 and ring gear R2 of thesecond planetary gear set 16 are respectively connected to the secondelectric motor MG2 and output gear 30, and to the housing 26 through thebrake BK. The sun gear S1 and the ring gear R2 are selectively connectedto each other through the clutch CL. The clutches C1 and C2 areconnected to each other. In the hybrid vehicle drive system 180 shown inFIG. 24, the sun gear S1, carrier C1 and ring gear R1 of the firstplanetary gear set 14 are respectively connected to the first electricmotor MG1, output gear 30 and engine 12, while the sun gear S2, carrierC2 and ring gear R2 of the second planetary gear set 16 are respectivelyconnected to the second electric motor MG2, to the housing 26 throughthe brake BK, and to the output gear 30. The ring gear R1 and thecarrier C2 are selectively connected to each other through the clutchCL. The carrier C1 and ring gear R2 are connected to each other.

The hybrid vehicle drive systems shown in FIGS. 22-24 are identical witheach other in that each of these hybrid vehicle drive systems isprovided with the first differential mechanism in the form of the firstplanetary gear set 14 and the second differential mechanism in the formof the second planetary gear set 16, 16′, which have four rotaryelements (whose relative rotating speeds are represented) in thecollinear chart, and is further provided with the first electric motorMG1, second electric motor MG2, engine 12 and output rotary member(output gear 30) which are connected to the respective four rotaryelements, and wherein one of the four rotary elements is constituted bythe rotary element of the first planetary gear set 14 and the rotaryelement of the second planetary gear set 16, 16′ which are selectivelyconnected to each other through the clutch CL, and the rotary element ofthe second planetary gear set 16, 16′ selectively connected to therotary element of the first planetary gear set 14 through the clutch CLis selectively fixed to the housing 26 as the stationary member throughthe brake BK, as in the hybrid vehicle drive system shown in FIGS. 4-7.The hybrid vehicle drive control device of the present inventiondescribed above by reference to FIG. 9 and the other figures is suitablyapplicable to the drive systems shown in FIGS. 22-24.

As described above, the illustrated embodiments are configured such thatthe hybrid vehicle is provided with: the first differential mechanism inthe form of the first planetary gear set 14 and the second differentialmechanism in the form of the second planetary gear set 16, 16′, whichhave the four rotary elements as a whole when the clutch CL is placed inthe engaged state (and thus the first planetary gear set 14 and thesecond planetary gear set 16, 16′ are represented as the four rotaryelements in the collinear charts such as FIGS. 4-7); and the engine 12,the first electric motor MG1, the second electric motor MG2 and theoutput rotary member in the form of the output gear 30 which arerespectively connected to the four rotary elements. One of the fourrotary elements is constituted by the rotary element of theabove-described first differential mechanism and the rotary element ofthe above-described second differential mechanism which are selectivelyconnected to each other through the clutch CL, and one of the rotaryelements of the first and second differential mechanisms which areselectively connected to each other through the clutch CL is selectivelyfixed to the stationary member in the form of the housing 26 through thebrake BK. The drive control device is configured to change the outputtorque of the engine 12 when the operating states of the clutch CL andthe brake BK are changed in the respective opposite directions, namely,when the clutch-to-clutch control to switch the clutch and the brake torespective different operating states is implemented. According to theillustrated embodiments wherein the output torque of the engine 12 iscontrolled, it is possible to reduce occurrence of problems such as anexcessive rise of the speed of the electric motor, as well as avariation of the vehicle drive force, during the control to change theoperating states of the clutch and the brake in the respective oppositedirections to switch the vehicle drive mode from one of the drive modesto another. Namely, the illustrated embodiments provide a drive controldevice in the form of the electronic control device 40 for a hybridvehicle, which permits reduction of occurrence of such problems uponswitching of the vehicle drive mode from one mode to another.

The output torque of the engine 12 is increased when the clutch CL whichhas been held in the released state and the brake BK which has been heldin the engaged state are respectively brought into the engaged state andthe released state. Accordingly, it is possible to reduce occurrence ofthe problems such as the excessive rise of the speed of the electricmotor, as well as the variation of the vehicle drive force, during thereleasing action of the brake BK and the engaging action of the clutchCL to switch the vehicle drive mode from one drive mode to another.

The first planetary gear set 14 is provided with a first rotary elementin the form of the sun gear S1 connected to the first electric motorMG1, a second rotary element in the form of the carrier C1 connected tothe engine 12, and a third rotary element in the form of the ring gearR1 connected to the output gear 30, while the second planetary gear set16 (16′) is provided with a first rotary element in the form of the sungear S2 (S2′) connected to the second electric motor MG2, a secondrotary element in the form of the carrier C2 (C2′), and a third rotaryelement in the form of the ring gear R2 (R2′), one of the carrier C2(C2′) and the ring gear R2 (R2′) being connected to the ring gear R1 ofthe first planetary gear set 14. The clutch CL is configured toselectively connect the carrier C1 of the first planetary gear set 14and the other of the carrier C2 (C2′) and the ring gear R2 (R2′) whichis not connected to the ring gear R1, to each other, while the brake BKis configured to selectively fix the other of the carrier C2 (C2′) andthe ring gear R2 (R2′) which is not connected to the ring gear R1, to astationary member in the form of the housing 26. Accordingly, it ispossible to reduce occurrence of problems when the hybrid vehicle drivesystem 10 having a highly practical arrangement is switched from one ofthe drive modes to another.

While the preferred embodiments of this invention have been described byreference to the drawings, it is to be understood that the invention isnot limited to the details of the illustrated embodiments, but may beembodied with various changes which may occur without departing from thespirit of the invention.

NOMENCLATURE OF REFERENCE SIGNS 10, 100, 110, 120, 130, 140, 150, 160,170, 180: Hybrid vehicle drive system 12: Engine 14: First planetarygear set (First differential mechanism) 16, 16′: Second planetary gearset (Second differential mechanism) 18, 22: Stator 20, 24: Rotor 26:Housing (Stationary member) 28: Input shaft 30: Output gear (Outputrotary member) 32: Oil pump 40: Electronic control device (Drive controldevice) 42: Accelerator pedal operation amount sensor 44: Engine speedsensor 46: MG1 speed sensor 48: MG2 speed sensor 50: Output speed sensor52: Wheel speed sensors 54: Battery SOC sensor 56: Engine controldevice 58: Inverter 60: Hydraulic control unit 70: Drive modedetermining portion 72: Electric motor operation control portion 74:Clutch engagement control portion 76: Brake engagement control portion78: Engine drive control portion BK: Brake CL: Clutch C1, C2, C2′:Carrier (Second rotary element) MG1: First electric motor MG2: Secondelectric motor OWC: One-way clutch P1, P2, P2′: Pinion gear R1, R2, R2′:Ring gear (Third rotary element) S1, S2, S2′: Sun gear (First rotaryelement)

1. A drive control device for a hybrid vehicle provided with: adifferential device which includes a first differential mechanism and asecond differential mechanism and which has four rotary elements; and anengine, a first electric motor, a second electric motor and an outputrotary member which are respectively connected to said four rotaryelements, and wherein one of said four rotary elements is constituted bya rotary component of said first differential mechanism and a rotarycomponent of said second differential mechanism which are selectivelyconnected to each other through a clutch, and one of the rotarycomponents of said first and second differential mechanisms which areselectively connected to each other through said clutch is selectivelyfixed to a stationary member through a brake, said drive control devicecomprising: an engine drive control portion configured to temporarilychange an output torque of said engine when operating states of saidclutch and said brake are changed in respective opposite directions toswitch a vehicle drive mode from one of drive modes to another.
 2. Thedrive control device according to claim 1, wherein said engine drivecontrol portion increases the output torque of said engine when saidclutch which has been held in a released state and said brake which hasbeen held in an engaged state are respectively brought into an engagedstate and a released state.
 3. The drive control device according toclaim 1, wherein said first differential mechanism is provided with afirst rotary element connected to said first electric motor, a secondrotary element connected to said engine, and a third rotary elementconnected to said output rotary member, while said second differentialmechanism is provided with a first rotary element connected to saidsecond electric motor, a second rotary element, and a third rotaryelement, one of the second and third rotary elements of the seconddifferential mechanism being connected to the third rotary element ofsaid first differential mechanism, and wherein said clutch is configuredto selectively connect the second rotary element of said firstdifferential mechanism, and the other of the second and third rotaryelements of said second differential mechanism which is not connected tothe third rotary element of said first differential mechanism, to eachother, while said brake is configured to selectively fix the other ofthe second and third rotary elements of said second differentialmechanism which is not connected to the third rotary element of saidfirst differential mechanism, to the stationary member.